Tree Species Composition, Richness and Diversity in the Northern Guinea-Savanna Taraba State, Nigeria

Abstract

The study investigated tree species composition, diversity and abundance in the Guinea savanna ecosystem, Taraba State, Nigeria. Three transects with a distance of 500 m apart were used for the study. Four sample plots of 25 m x 25 m size were laid in alternate positions along each transect at 250 m intervals. Identification of trees/shrubs was carried out in the forest reserves. Biodiversity indices such as; Shannon-Wiener diversity index, Species evenness, Simpson’s diversity index, Margalef’s richness index and Menhinick’s diversity index, were estimated at the end of the study. The result of floristic diversity assessment showed that the two forest reserves were able to conserve trees/shrubs species diversity. This was reflected by the value obtained for diversity indices for the two land use types: Shannon- Weinner (3.29, 3.08), species evenness (0.47, 0.49), Simpson (0.95, 0.93), Margalef (6.83, 6.49), Minhinck’s index (2.09, 1.79) for Sonkpa and Jabwanje forest reserves respectively. The density of fruit trees/shrubs encountered in the two forest reserves were (279, 414) which accounted for (47% and 56%) of the total woody population in Sonkpa and Jabwanje forest reserves respectively. Among the prominent fruit trees/shrubs encountered were Nauclea latifolia, Gardenia aqualla, Annona senegalensis, Prosopis africana, Vitellaria paradoxa, Vitex doniana, Strychnos innocua.  However, the absence of Irvingia gabonensis and lower density of Afzelia africana was an indication that some important species are already going to extinction while others are endangered.  Hence, the State government should, intensify the management of savanna forest by controlling the intensity of tree harvesting, stop illegal felling and encourage enrichment planting. Genetic improvement through germplasm collection and propagation studies should be carried out on the under exploited edible fruit species for genetically improved cultivars production.